This application claims the priority of Japanese Patent Application No. 11-266712 filed on Sep. 21, 1999, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image stabilizing apparatus, disposed within an optical apparatus such as monocular, binoculars, and video camera, for preventing optical images from being observed in a blurred state due to the fluctuation in emission angle of luminous flux from an observation object with respect to the optical axis of the optical apparatus when the optical apparatus is vibrated.
2. Description of the Prior Art
When an optical apparatus aimed at optical observation, such as monocular and binoculars, is operated as being held with a hand, when the optical apparatus is used in an airplane, vehicle, or the like in particular, the vibration or rocking of the airplane, vehicle, or the like is transmitted to the optical apparatus, so that the emission angle of luminous flux from an observation object with respect to the optical axis fluctuates, whereby the optical image to be observed often deteriorates. Even if the vibration transmitted to such an optical apparatus has a small amplitude, the angle of fluctuation with respect to the optical axis is enlarged since the field of view is narrow in the monocular, binoculars, and the like, and since the observation object is viewed under magnification therein. Therefore, even at the time of rocking with a relatively low angle fluctuating speed, the observation object may rapidly move within the field of view, and go out of sight when the angle of fluctuation is large, which is inconvenient. At the time of rocking with a relatively high angle fluctuating speed, on the other hand, the angle fluctuating speed of the image of observation object is observed as being increased by the power of optical apparatus even when the fluctuation angle is relatively small, whereby the image blurs and deteriorates, which is inconvenient.
Conventionally, various image stabilizing apparatus for preventing observation images from being deteriorated due to fluctuations in the emission angle of luminous flux with respect to the optical axis due to the vibration and rocking transmitted to optical apparatus have been proposed.
For example, Japanese Patent Publication No. 57-37852 discloses binoculars comprising therein anti-vibration means utilizing a rotary inertial member (gyro motor) in order to correct the blur of observation images in the binoculars.
Namely, according to this technique, an erect prism is disposed on the optical axis between an objective lens and an eyepiece of the binoculars and is secured onto gimbal suspension means, such that the erect prism is held in substantially the same posture even when the binoculars are vibrated due to camera shake or the like, so as to prevent the observation image of binoculars from blurring.
In such a conventional technique utilizing a rotary inertial member and gimbal suspension means, while images can be stabilized with a high accuracy, a high-speed rotary member is required for yielding a large inertial force within a small space, and a high precision is needed since the vibration generated by the rotary member itself has to be reduced. Such demands for smaller size, higher speed, and higher precision are problematic in that they impose inconveniences in terms of cost, life, time required for attaining a necessary inertial force after the power is turned on, and the like. If the effective diameter of objective lenses is made greater along with the increase in power or resolution of binoculars, then the erect prism becomes larger, whereby a large inertial force is required, which enhances the above-mentioned problems, and the power consumption increases along therewith.
Therefore, the assignee of the present application has proposed an image stabilizing apparatus (Japanese Unexamined Patent Publication No. 6-250100) in which an angular velocity sensor is mounted to gimbal suspension means in place of above-mentioned rotary inertial member, and the pivoting of the gimbal suspension means is controlled according to the output value from the angular velocity sensor, so as to fix the posture of the erect prism with respect to the earth (inertial system). According to this apparatus, the erect prism held with the gimbal suspension means basically has an inertial force. In particular, its posture-keeping capability against vibrations with a relatively large amplitude is high with respect to high-speed vibrations with a high vibration frequency. Therefore, the control power for the rotational position according to the angular velocity sensor can be kept small. In other image stabilizing apparatus which drive varn-angle prisms or lenses, however, active driving sections are needed, and it is necessary for the driving sections to be operated at a high speed in order to correct a large amplitude in high-frequency vibrations, whereby correction in a wide angle range is difficult.
The above-mentioned gimbal suspension means is pivoted by an actuator such as motor about two pivotal axes extending sidewise and vertical directions of the optical apparatus, respectively. The actuator is driven by PWM (Pulse Width Modulation) control, which is excellent in response and is favorable in terms of power utilization efficiency.
In the PWM control, a pulse waveform is outputted from pivoting control means to a driving circuit, and an actuator is driven with a power corresponding to the pulse width of output waveform. Consequently, there is a problem that, if the power voltage of the driving circuit drops while the apparatus is in use as in the case employing a battery power source, then the actuator driving power may decrease, whereby the aimed pivoting control cannot be carried out.
By contrast, if a regulator is disposed on the power source side of the driving circuit, so as to supply a constant voltage to the driving circuit, then the actuator driving power can be kept constant. In such a case, however, a high power type regulator is necessary when the actuator has a heavy load, which yields no merits in terms of size, heat generation, cost, and the like in small-size optical apparatus, in particular.
In view of such circumstances, it is an object of the present invention to provide an image stabilizing apparatus configured such that an actuator for pivoting gimbal suspension means is driven under PWM control by way of a driving circuit, in which, even when the power voltage of the driving circuit drops while the apparatus is in use, the actuator driving power can be kept from decreasing, so as to carry out the aimed pivoting control.
The present invention provides an image stabilizing apparatus mounted in an optical apparatus having a monocular or binocular optical system in which an erect prism is disposed between an objective lens and an eyepiece, whereas the objective lens and eyepiece of the optical system are secured within a case;
the image stabilizing apparatus comprising:
gimbal suspension means, adapted to pivotally attach the erect prism to the case, having two pivotal axes extending sidewise and vertical directions of the optical apparatus, respectively;
an actuator for pivoting the gimbal suspension means about the two pivotal axes;
pivoting control means for driving the actuator under PWM control by way of a driving circuit and controlling the pivoting of the gimbal suspension means about the two pivotal axes so as to fix the erect prism with respect to an inertial system; and
pulse width correcting means for enhancing, when a power voltage of the driving circuit drops, a pulse width of a waveform outputted from the pivoting control means to the driving circuit.
Preferably, in this case, the correction rate of pulse width is set to the reciprocal of drop rate of power voltage.
While a maximum limit value is set for pulse width in PWM control in general, it is preferred that the image stabilizing apparatus further comprise maximum limit value correcting means for enhancing the maximum limit value.
Preferably, in this case, a correction rate of the maximum limit value is set to the same value as the correction rate of pulse width.